We propose a prospective study of homosexual male patients with epidemic Kaposi's Sarcoma (KS), opportunistic infections (OI) and generalized persistent lymphadenopathy (LA) and four groups of unaffected control individuals. The different study groups will be investigated for risk factors with regard to lifestyle. The emphasis of the investigation concerns the identification of the nature of the acquired immunodeficiency syndrome "AIDS", and the relationship between immunogenetic host factors (i.e. HLA-DR5 and Gm-allotypes) and susceptibility to disease development. The studies will focus on the identification of particular immunological parameters or combinations of these which may have predictive value with regards to the development and progression of the different disease entities. Investigations of manipulation of immunological responses in vitro with Interferon and Interleukin-2 will be performed and followed by therapeutic trials with in vivo therapy with Interferon and Interleukin-2. Lymphocyte replacement by allogeneic lymphocyte infusion of HLA identicial and HLA incompatible normal lymphocytes will also be investigated. In addition, we will investigate cell lines of lymphoid and non-lymphoid origin from selected patients for unique particles (e.g. virus) by transmission electron microscopy. A special study aimed at cultivation of pneumocystis carinii is also planned.